1. Field of the Invention
The present invention generally relates to an improved mounting device and mounting arrangement for apparatus used in metal melting, refining and processing, for example, steel making in an electric arc furnace (EAF), and more particularly, to an mounting arrangement for an auxiliary burner or lance relatively close to a molten metal bath to increase its efficiency.
2. Description of Background Art
An electric arc furnace makes steel by using an electric arc to melt one or more charges of scrap metal which is placed within the furnace. The scrap is charged by dumping it into the furnace through the roof from buckets which also may include charged carbon and slag forming materials. The arc melts the scrap into a molten pool of metal, called an iron carbon melt, which accumulates at the bottom or hearth of the furnace. After a flat bath has been formed by melting of all the scrap introduced, the electric arc furnace enters a refining or decarburizing phase. In this phase, the metal continues to be heated by the arc until the slag forming materials combine with impurities in the iron carbon melt and rise to the surface as slag. When the iron carbon melt reaches a boiling temperature, the charged carbon in the melt combines with any oxygen present in the bath to form carbon monoxide bubbles which rise to the surface of the bath. Generally, at this time supersonic flows of oxygen are blown at the bath with either lances or burners to produce a decarburization of the bath by the oxidation of the carbon contained in the bath. By simultaneously boiling the bath and injecting it with oxygen, the carbon content of the bath is reduced to under 2% carbon whereby the iron carbon melt becomes steel. The carbon in the steel bath is thereafter further reduced until the grade of steel desired is produced, down to less than 0.2% for low carbon steels.
To assist in the steel making process, auxiliary burners or lances can be used for the addition of thermal energy by the combustion of fuel, the injection of oxidizing gas for melt refining, foamy slag production or post combustion of carbon monoxide, and the injection of particulates for slag and foamy slag production. In many instances, the oxidizing gas is introduced as a high velocity stream that may exceed sonic velocities. Laval nozzles, or other supersonic nozzle types, are usually used in the production of high velocity streams of oxidizing gas for injection into a steel making furnace. These supersonic gas flows are produced by the converging/diverging shape of the nozzle which at above a critical pressure causes the gas flow though the nozzle to become supersonic. It is also highly desirable to provide a subsonic flow of oxidizing gas for the burning of fuel, including regular fuel and carbon monoxide for post combustion, for the addition of auxiliary thermal energy, and the supersonic oxygen flow for providing oxygen in iron melt decarburization, assisting in foamy slag production or post combustion of carbon monoxide.
An auxiliary oxy/fuel burner which is useful in the process of steel production in electric arc furnaces and which provides subsonic and supersonic flows of oxygen through the same centrally located conduit is shown to advantage in a technical publication entitled "Advanced Burner Design" by V. Shver, T. Pulliam, and M. Cohen (Shver, et al. I) dated November 1997. This burner is manufactured and commercially sold by Process Technology International, Inc. of Tucker, Ga., the assignee of the present invention. The subsonic flow is produced by providing a pressure in the supply conduit lower than the critical pressure of the supersonic nozzle being used in the conduit. When supersonic oxygen is needed, the pressure in the supply conduit is increased to above the critical pressure. The disclosure of Shver, et al. I is hereby incorporated by reference.
Another burner with the capability to introduce supersonic or subsonic oxidizing gas into an electric arc furnace is illustrated in U.S. Ser. No. 09/251,193, entitled "Method and Apparatus for Improved EAF Steelmaking", filed Feb. 15, 1999 in the name of V. Shver, and assigned commonly with the present application. Shver discloses an annular nozzle for producing a supersonic oxygen flow surrounding a carbon injection conduit forming a portion of a nozzle in a fluid cooled combustion chamber of the burner.
Still another burner with the capability to introduce supersonic or subsonic oxidizing gas into an electric arc furnace is illustrated in U.S. Ser. No. 09/459,303 entitled "Improved Method and Apparatus For Metal Melting, Refining and Processing", filed Dec. 10, 1999 in the names of V. Shver, et al. (Shver, et al. II), and assigned commonly with the present application. Shver, et al. II discloses a supersonic oxygen conduit in a side by side arrangement with a carbon injection conduit forming a portion of a nozzle in a fluid cooled combustion chamber of the burner.
Additionally, there are many other burners and lances which provide a supersonic oxidizing gas lancing capability and which provide for the introduction of other materials for use in an electric arc furnace.
The supersonic lancing mode is used in one instance for melt refining because the flow of oxygen must penetrate the molten metal in the hearth of the firnace. The increased velocity of the gas from accelerating it to a supersonic condition increases its momentum and thus depth of penetration into the melt. Another technique to increase the penetrating power of an oxidizing gas flow is to increase the flow rate by the use of a larger supersonic nozzle. While this advantageous to some extent, an excess of oxidizing gas is detrimental to the furnace components and the higher pressures needed for the larger nozzles rapidly become uneconomic.
The mounting of these burners and lances have generally been either through openings in the furnace which are used for other purposes, such as the slag door, roof holes or the EBT access panels, or in greater numbers through specially made openings in the water cooled panels of the side wall of the furnace. The specially made side wall openings allow the burners to be strategically mounted, for example, where there are cold spots in the furnace, or other desired places, possibly for the introduction of process materials. To improve the penetrating power and efficiency of the supersonic oxidizing gas flows from the burners, the mountings of the burners in the furnace side wall have been as far down on the side panels as possible. However, there has been a limit to the mounting of the burners in proximity to the melt because of the structure of many present day furnaces.
The hearth of the furnace is made of refractory materials to contain the molten metal during steel processing. The hearth of the furnace forms a step with the water cooled panels of the furnace side wall where they connect. In the past, the burners have been mounted high enough and at an suitable angle on the side walls where the introduced flows of super sonic oxygen or other materials will miss the edge of the step. Even for those instances where such flows miss the step, the is some deterioration of the refractory by the highly reactive oxidizing gas flowing closely past it. For apparatus providing supersonic oxidizing gas flow this means the mounting angle and flow rates are not only dictated by the steel making process requirements but also by the structure of the furnace.
Therefore, there is a need to mount burners and lances with supersonic oxidizing gas capability closer to the molten metal and directed more to the center of the furnace so they can be more efficient in operation.
There is also a need to mount these burners and lances at optimum angles, to operate them at optimum flow rates and at optimum distances from the melt.